1. Field of the Invention
The present invention relates to a high strength structural member made of Al-alloy which has been produced through a powder metallurgical process.
2. Description of the Prior Art
In an internal combustion engine for motor vehicles, in order to realize reduction of weight of a vehicle body aluminium-alloy materials have been positively employed, and especially it is effective also for reducing an inertial force to form moving parts such as connecting rods, pistons and the like of aluminium-alloy materials. Such moving parts are required to have heat-resistivity and high strength because they are used under a severe condition at a high temperature, and in order to fulfil this requirement, there is a tendency of employing powder metallurgical products in which alloy elements can be added with a large freedom.
Al-alloy for powder metallurgical products in which high proportions of Si, Fe and other elements were added to Al aiming at improvements in a high-temperature strength, a Young's modulus, an abrasion-proofness and a heat-resistivity, was previously proposed in Japanese Patent Application No. 59-166979 which was filed by the Assignee of this application.
However, as a result of various investigations on such high strength aluminium-alloys, it was concluded that in order to apply the aluminium-alloy to a structural member for which a high fatigue strength is required such as a crank shaft, it is desirable to contemplate further increase of strength.
For the purpose of satisfying this requirement, it may be conceived to produce a thick surface film on the surface of the member by hardening anodic oxidation treatment that is known as a surface hardening process for aluminium alloy, but this treatment is hard to be employed for the reasons that it does not contribute to improvement in strength of a member although it is effective for improving an abrasion resistivity. The expense for the treatment is high.